1. Field of the Invention
The present invention relates generally to ceiling fans and, more particularly, to a method and apparatus for balancing ceiling fans.
2. Related Art
Ceiling fans have become an increasingly popular supplementary means of conditioning air within both commercial and residential buildings. Notwithstanding the widespread use of ceiling fans, one continuing problem which faces ceiling fan designers is the tendency of ceiling fans to "wobble", or pivot about the point of suspension, due to fan blade imbalance. Although this problem is more prevalent in ceiling fans suspended from a ceiling by a canopy and downrod arrangement, ceiling fan wobble may also exist in other configurations such as low profile ceiling fans which are mounted in close proximity to the ceiling. Fan blade imbalance and the associated ceiling fan wobble may result from a variety of discrepancies associated with the ceiling fan blades including variations in blade pitch angle, dihedral angle, uneven circumferential spacing between adjacent blade pairs, blade warpage and uneven radial spacing of the blades from the vertical axis of rotation. Ceiling fan wobble and the associated vibration creates undesirable noise, is visually distracting and may adversely affect the service life of the ceiling fan.
One known method of balancing ceiling fans includes the steps of temporarily attaching a test clip, which may resemble a "clothespin", to the leading edge of one of the fan blades, then operating the fan and observing the fan wobble. This process is repeated for each of the fan blades, with the wobble being observed during each test run of the fan. The test clip is then positioned on the leading edge of the blade producing the minimum wobble at a position adjacent the blade iron or attachment bracket. The fan is then operated several additional times, with the test clip being move radially outward on the blade by a small increment after each test run. This is repeated until the optimum radial position of the test clip, with respect to fan wobble, is determined. The test clip is then replaced with a self-adhesive balance weight applied to the top surface of the blade, along the blade centerline, at the optimum radial position identified by operating the fan with the test clip attached to one of the blades.
The foregoing trial-and-error method of balancing a ceiling fan is relatively simple and inexpensive to implement, and may be advantageously used for balancing ceiling fans having an even number of fan blades, such as four blades. However, this method is less effective in balancing ceiling fans having an odd number of blades, such as five blades. For instance, if one of the five blades is heavy, there is no blade diametrically opposed to the heavy blade. Accordingly, if the foregoing balancing method is completed, it is very likely that the ceiling fan will still experience wobble. Although it is known to repeat the process and add a balance weight to a second blade, the identification of the second blade may be time consuming and may not yield the optimum results. Since the application of a weight to the first blade is inherently deficient with respect to balancing a fan having an odd number of blades, it is difficult to overcome this built-in error and to identify the proper blade, and radial position on the blade, for attachment of a second balance weight.
Another disadvantage of the foregoing method is the shape and placement of the test clip on the blade. The known test clip which is commonly used does not have an aerodynamic shape but instead may resemble a clothespin as mentioned previously and therefore may create a relatively significant interruption of the airflow passing over the blade. This problem of airflow disturbance is amplified by placing the clip on the leading edge of the blade, rather than on the trailing edge of the blade, for instance. Accordingly, airflow-induced vibrations may occur which may mask the optimum position for placement of the test clip and balance weight. Yet another disadvantage of the foregoing method of balancing ceiling fans is that the test runs of the ceiling fan are conducted with the test clip positioned on the leading edge of the blade but the replacement balance weight is attached to the blade along the blade centerline. Accordingly, even if the balance weight is attached at the radial position identified by the test clip and has about the same weight as the test clip, the balancing effect of the test clip may not be duplicated.
Other known methods of balancing ceiling fans include attaching an annular ring to the ceiling fan, with the ring having a cavity containing a variety of weights, or attaching an annular tube containing a viscous fluid to the ceiling fan, with the weights or fluid being distributed by centrifugal force and counteracting any rotational imbalance in the fan. However, these devices add weight, cost and complexity to the fan, and may not be visually appealing. In view of the foregoing deficiencies associated with known methods of balancing ceiling fans, there remains a need for a simple, economic and efficient method and apparatus for balancing ceiling fans.